1. Field of the Invention
The invention relates generally to low ampere-high temperature switches. The invention relates more specifically to the contact designs for such switches.
2. Description of Prior Art
Mechanical switches for carrying low current at high temperature are often problematic. Low current is generally meant to include the range of 0.001 to 0.050 amp. High temperature is generally meant to include 500.degree. F.-900.degree. F. High temperature prevents the use of certain plating materials, due to softening, and the low current does not provide sufficient energy, or spark, at the contacts to burn away contaminants that can occur on all contact materials except the most noble materials.
Because many plating materials become soft at high temperatures, troughing of the contact point, wherein a groove is formed in the mating surfaces as seen in FIG. 1, may occur on the softer of the contact surfaces, typically the moveable contact which is often plated with a thicker layer of a noble material such as gold. Troughing causes loss of wiping action when the moveable contact 13 makes contact with the stationary contact 15. Loss of wiping means contaminants will not be moved away from the contact area, resulting in less efficient current flow. Troughing is exacerbated by plating thickness where most softening of contact material occurs. Troughing also increases the mechanical contact movement which can change operating characteristics. Mechanical interlocking of the contacts in the trough also can cause complete loss of switch function.
Therefore, it would be desirable to have a switch design which can retain good electrical contact characteristics while operating at low current and high temperatures, and be resistant to the softening and troughing problems just described.